A predictive approach of the influence of the operating parameters on the size of polymer particles synthesized in a simplified microfluidic system

Monodisperse and size-controlled spherical polymer particles were synthesized by in situ photopolymerization of O/W monomer emulsions. Monomer droplets were produced without surfactant or pretreatment at a needle tip in a simplified axisymmetric microfluidic device. The effect of the viscosity of the continuous phase on the particle size was studied. The system operated in the dripping mode, at a low Reynolds number. A dimensionless master curve describes the particle diameter as a function of the needle inner diameter as well as velocity and viscosity ratios of continuous and dispersed phases. An empirical law predicts the particle size. The normalized particle diameter depends upon the ratio of the capillary numbers of continuous and dispersed phases with an exponent equal to -0.22.     

Application of the perturbed chain SAFT equation of state to complex polymer systems using simplified mixing rules

A simplified perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state is applied to polymer systems that include a variety of non-associating (esters, cyclic hydrocarbons), polar (ketones) as well as associating (amines, alcohols) solvents. The solvent pure-component parameters that are not available in the literature are estimated by correlating vapor-pressure and liquid-density data. The performance of the simplified PC-SAFT is compared to the original PC-SAFT equation of state for polymer systems of varying complexity. It is shown that the applied simplification is not at the expense of the accuracy of equation of state, while the computational time and complexity are significantly reduced, especially for associating systems. With no binary interaction parameter, simplified PC-SAFT is successfully able to predict vapor–liquid equilibria of polymers with non-associating solvents. In the case of associating solvents, a small binary interaction parameter k_ij is usually needed for the satisfactory correlation of the experimental data.     

A new approach to NMR chemical shift additivity parameters using simultaneous linear equation method

A new approach to NMR chemical shift additivity parameters using simultaneous linear equation method has been introduced. Three general nitrogen-15 NMR chemical shift additivity parameters with physical significance for aliphatic amines in methanol and cyclohexane and their hydrochlorides in methanol have been derived. A characteristic feature of these additivity parameters is the individual equation can be applied to both open-chain and rigid systems. The factors that influence the (15)N chemical shift of these substances have been determined. A new method for evaluating conformational equilibria at nitrogen in these compounds using the derived additivity parameters has been developed. Conformational analyses of these substances have been worked out. In general, the results indicate that there are four factors affecting the (15)N chemical shift of aliphatic amines; paramagnetic term (p-character), lone pair-proton interactions, proton-proton interactions, symmetry of alkyl substituents and molecular association.     

A simplified approach to vapor–liquid equilibria calculations with the group-contribution lattice-fluid equation of state

Equations of state that are based on the lattice-statistics approach use Guggenheim's quasi-chemical approximation to describe the non-randomness in the mixture due to the energetic interactions between the molecules. For ternary and higher-component systems the non-randomness expression is complex and requires an iterative calculation procedure. We have shown that the non-randomness parameters play a negligible role in the application of the GCLF-EoS model (based on the Panayiotou–Vera EoS) for predicting vapor–liquid equilibria. Omission of the non-randomness parameters from such calculations can significantly improve the computation efficiency. Binary, ternary, and quaternary vapor–liquid equilibria predictions were made including polystyrene, polyvinyl acetate, polyethylene, and polypropylene in polar and non-polar solvents to test the theory.     

A simple method for evaluation of parameters of the Bender equation of state from experimental data

A simple numerical method for evaluation of parameters (constants) of Bender equation of state for pure fluids is proposed. The minimisation of the objective function leads to a set of linear equations. The method employs experimental data on state behaviour (p–ρ–T) of fluid phases, vapour–liquid equilibrium data (saturated vapour pressures and orthobaric densities), second virial coefficients, and the coordinates of the gas–liquid critical point. Results of the tests using data for two fluids (methane and n-pentane) are presented.     

A simplified approach for the coupling of excitation energy transfer

A simplified approach for computing the electronic coupling of nonradiative excitation-energy transfer is proposed by following Scholes et al.’s construction on the initial and final states [G.D. Scholes, R.D. Harcourt, K.P. Ghiggino, J. Chem. Phys. 102 (1995) 9574]. The simplification is realized through defining a set of orthogonalized localized MOs, which include the polarization effect of the charge densities. The method allows calculating the coupling of both the singlet-to-singlet and triplet-to-triplet energy transfer. Numerical tests are performed for a few of dimers with different intermolecular orientations, and the results demonstrate that Coulomb term are the major contribution to the coupling of singlet-to-singlet energy transfer whereas in the case of triplet-to-triplet energy transfer, the dominant effect is arisen from the intermolecular charge-transfer states. The present application is on the Hartree-Fock level. However, the correlated wavefunctions which are normally expanded in terms of the determinant wavefunctions can be employed in the similar way.     

Quasichemical approach to crosslinked polymer solutions and the swelling equation for polycondensation networks

The change of free enthalpy and the chemical potential of solvent for mixing of solvent with crosslinked structures formed by stepwise reactions of the polycondensation type has been derived by an adaptation of the quasichemical equilibrium method. Each monomer unit is supposed to bear a different number of crosslinkable contact points, the coupling of which gives rise to chemical bonds, and of uncrosslinkable contact points, involved in interactions with the solvent, which may be of different type. The results are used to analyze the effect of network topology on the parameters of the swelling equation, particularly on a parameter characterizing the network composition. This parameter may be obtained from analytical data or by using the crosslinking statistics; and model calculations show how it varies with monomer conversion.     

A CFD based approach to assess the effect of environmental parameters on decay product-aerosol attachment coefficient

Journal of Radioanalytical and Nuclear Chemistry - Attachment of decay products of radon and thoron to environmental aerosols is an important process which govern the inhalation dose. This process...     

A simplified integral equation for adsorption of gas mixtures on heterogeneous surfaces

Summary The multiple integral representing the overall isotherm for adsorption of gas mixtures on heterogeneous surfaces is transformed to a single integral, which is promising for predicting the mixed-gas adsorption by means of single-gas adsorption parameters. This transformation is possible when the adsorption energies of components for various adsorption sites show a certain type of correlation.

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Eine vereinfachte Integralgleichung für die Adsorption von Gasmischungen auf heterogenen Oberflächen

Zusammenfassung Das multiple Integral, das die Adsorption von Gasmischungen auf heterogenen Oberflächen darstellt, wurde zu einem einfachen Integral transformiert, das zur Voraussage der Adsorption von Gasgemischen mittels der Einzelgas-Adsorptionsparameter geeignet sein sollte. Diese Transformation ist dann möglich, wenn die Adsorptionsenergien der Komponenten einem bestimmten Korrelationstyp angehören.

     

A new cubic simplified perturbed hard-body equation of state

A new cubic equation of state (EOS) was developed in this study for vapor-liquid equilibrium (VLE) calculations of nonpolar fluids. The repulsive term of this EOS reexpressed the results of Walsh and Gubbins (1990) from their modified thermodynamic perturbation theory of polymerization into a simple form in which a non-spherical parameter was employed to account for the different shapes of molecules. The repulsive compressibility factors calculated from this EOS agree well with the molecular simulation data for various kinds of hard bodies ranging from a single hard sphere to tangent or fused long chain molecules. A simple attractive term was then coupled with the repulsive to complete the EOS in a cubic form. Equation parameters were determined for a diversity of nonpolar real fluids. These parameters were expressed in generalized forms for engineering computations. Satisfactory results from this EOS on the saturated properties of pure nonpolar fluids were obtained. This EOS was also extended to calculate the VLE of nonpolar fluid mixtures. The results are again satisfactory over wide ranges of temperature and pressure.     

A novel approach to the micropatterning of proteins using dewetting of polymer bilayers

The ability to control protein and cell positioning on a microscopic scale is crucial in many biomedical and bioengineering applications, such as tissue engineering and the development of biosensors. We propose here a novel, simple, and versatile method for the micropatterning of proteins. Micropatterned substrates are produced by the dewetting of a metastable polymer film on top of another polymer film. Selective adsorption, or micropatterning, of proteins can be achieved on such substrates by choosing pairs of polymers which differ in protein affinity. In this study, patterns were produced in bilayers of poly(methylmethacrylate) (PMMA) and polystyrene (PS), and of PMMA and octadecyltrichlorosilane (OTS). Fluorescence microscopy and atomic force microscopy (AFM) provide evidence that model proteins adsorb preferentially on isolated bio-adhesive (PS and OTS) micropatches in a protein-resistant (PMMA) matrix. "Inverse" protein patterns, containing non-adhesive (PMMA) islands in a protein-adhesive (PS) matrix can also be produced. Such micropatterned substrates could potentially be used in the development of biosensors and bioassays, and in the study of cell growth and motility.     

Effect of polymer polarity on the positronium formation

Positron annihilation lifetime spectra have been measured on styrene–methyl methacrylate, styrene–acrylonitrile, and styrene–butyl methacrylate copolymers. The results show that the longest lifetime τ₃ remains constant during extended PALS measurement in all experiment copolymers, and relative intensity I₃ decreases to a certain extent with measured time in weak polar copolymers and remain almost unchanged in strong polar copolymers as well as ST–BMA copolymers. The observed decrease in I₃ have been found to be unrelated to the microstructural change of copolymers, and, instead, to be more likely a result of the buildup of an electric field inside the copolymers during the prolonged PALS measurement. The field effect can result in the decrease of I₃ due to the increase in the positrons and electrons diffusing out of the spur, but the influence of the electric field on I₃ decrease with increasing the polarity of the copolymers and the softness of side groups of macromolecular chains in the copolymers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 435–442, 2000     

A simplified green chemistry approach to the Biginelli reaction using ‘Grindstone Chemistry’

Grindstone Chemistry--a greatly evolved version of Toda’s method of grinding solids together for solvent-free chemical reactions--has been described and its usefulness illustrated by the successful application of this technique to a simplified process for conducting the multi-component Biginelli reaction for the synthesis of physiologically active tetrahydropyrimidinones.     

Modeling phase equilibria of alkanols with the simplified PC-SAFT equation of state and generalized pure compound parameters

The simplified PC-SAFT equation of state has been applied to liquid–liquid, vapor–liquid and solid–liquid equilibria for mixtures containing 1- or 2-alkanols with alkanes, aromatic hydrocarbons, CO₂ and water. For the alkanols we use generalized pure compound parameters. This means that two of the physical pure compound parameters, m (segment number) and σ (segment diameter), are obtained from linear extrapolations, since m and mσ³, increase linearly with respect to the molar mass, and moreover, the two association parameters (association energy and association volume) were assumed to be constant for all alkanols. Only the dispersion energy is fitted to experimental data. Thus it is possible to estimate parameters for several 1- and 2-alkanols. The final aim is to develop a group contribution approach for PC-SAFT which is suitable for complex compounds, considering that the motivation of this project is to obtain a thermodynamic model which can be used in the development of sophisticated products such as pharmaceuticals, polymers, detergents or food ingredients. One of the severe limitations in applying SAFT-type equations of state to these compounds is that the procedure for obtaining the pure compound parameters is usually based on fitting to saturated vapor pressure and liquid density data over an extended temperature range. However, such data are rarely available for complex compounds. To verify the new pure compound parameters, comparisons to ordinary optimized alkanol parameters, where all five pure compound parameters were fitted to experimental liquid density and vapor pressure data, were made. The results show that the new generalized alkanol parameters from this work perform at least as well as other alkanol parameter sets.     

On simplified spherical harmonics equations for the radiative transfer equation

The radiative transfer equation (RTE) arises in a wide range of applications in sciences and engineering. Due to the high dimension and complicated form of the RTE, it is challenging to solve the equation directly. In the literature, several approximation methods were developed for the RTE. One approximation method, the simplified spherical harmonics (SP _N ) method, provides an efficient way to generate good approximate solutions of the RTE with high absorption and small geometries. The main purpose of the paper is to study well-posedness of the simplified spherical harmonics system. The weak formulation used in the proof of the solution existence and uniqueness provides a starting point for developing the Galerkin finite element method to solve the simplified spherical harmonics system.     

A computer automated structure evaluation (CASE) approach to calculation of partition coefficient

A Computer Automated Structure Evaluation (CASE) approach to the calculation of partition coefficient (log P) has been developed. A linear regression equation was obtained linking the log P value of molecules to some of their fragments as identified by a CASE analysis. The relationship was obtained for a database consisting of 935 compounds (r² = 0.93, s = 0.39, F(39, 895, 0.05) = 316.5). It was found that this approach produced accurate log P estimations even for complex molecules and, in general, gave better results than previously described techniques.     

Material parameters for the evaluation of PA welds using laser extensometry

The deformation and fracture behaviour of welded polymer slabs under tensile stress has been investigated by laser extensometry. The necessity of a position-sensitive materials testing method for describing the properties of welds of polymers, and the special requirements for the testing and evaluation method, have been introduced. The mechanical heterogeneity H representing the ratio of the local strain differences and the integral strain has proven to be a good indicator for the evaluation of welding quality. The information got by means of this testing method was then compared to results obtained conventionally.     

Determination of polarity parameters for liquid crystals using solvatochromic method in anisotropic and isotropic phases

The use of liquid crystals (LCs) as anisotropic solvents is desired for various potential applications and usually for other organic and inorganic compounds. In this work, solvent polarity parameters are obtained using a spectroscopic method for four LCs with a range of high and low dielectric anisotropy (?ε). Solvatochromic polarity parameters for these LCs were defined via Kamlet–Abboud–Taft polarity functions characterizing different temperatures and phases, isotropic and anisotropic, and using the Reichardt’s dye and 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio) phenolate standard probe. The investigated polarity parameters reveal the effects of LC media on the photo-physical behaviour of solute molecules in isotropic and anisotropic media. Subsequently, a new LC polarity parameter (Z_o) is introduced as an overall matrix anisotropy polarity parameter to characterize variation between isotropic and anisotropic phases. The values of Z_o are sorted from higher to lower dielectric anisotropies (?ε).